Some radiation sources exhibit wavelength drift over time in excess of that tolerable for many applications. This drift becomes increasingly important as the lifetimes over which these radiation sources are to be deployed increases. Factors such as temperature, age, operating power level, etc., all affect the output wavelength. Parameters such as the direction of the wavelength change, the degree of the change, and the percentage of the light being radiated at the different wavelengths may be monitored. By monitoring any or all these parameters, the radiation source may be controlled in accordance with known techniques to stabilize the output of the radiation source.
Such monitoring and stabilizing systems typically involve using a unit which is external to the radiation source itself. Such external units include crystal gratings, fiber gratings, spectrometers, and Fabry-Perot etalons, both straight and inclined. The grating systems include relatively large control units external to the radiation source. While etalon-based systems offer a more compact solution, so far these etalons are still separate units which may become improperly aligned, either with photodetectors or with optical elements required to direct and control the light onto the photodetectors. Further, etalons are very sensitive to angular alignment.
Etalons are very expensive, due to the tight requirements thereon to insure proper performance thereof. This expense is even further increased when the etalon is to be miniaturized. Thus, it would be advantageous to create a wavelength locker which did not rely on an etalon and which can provide continuous monitoring over an operational range.